Astronomy

Universe

all that exists everywhere, including all matter, energy, planets, stars, galaxies, and the space in which all of this exists

Planets

Mercury, Venus, earth, mars, Jupiter, Saturn, Uranus, Neptune

constellation

groups of stars that form a pattern in the sky

celestial sphere

an imaginary rotating sphere on which lie all objects of the night sky

ecliptic

path the sun and some other sky objects appear to take across the celestial sphere

retrograde motion

the path that planets appear to take in the sky due to their rotation around the sun

azimuth

the distance measured from north along the horizon

altitude

the angular height of a celestial object, measured from the horizon

galaxy

a collection of many billions of stars plus gas and dust, held together by gravity

Elliptical Galaxies

vary in shape from spherical to a flattened oval

make up 15-20%

spiral galaxies

look like a pinwheel, a flattened disk with a central bulge with 2 or 4 arms

Milkyway is spiral

barred spiral galaxies

similar to spiral, but have central bar pattern across the middle

irregular galaxies

have no defined shape

make up 10%

star cluster

a collection of stars held together by gravity

andromeda galaxy

closes galaxy to milky way

light year

a unit of distance equal to the distance light travels in one year

parallax

is the angle measured between two lines of sight, divided by two, used to calculate the distance to stars

Hertzsprung-Russell (HR) Diagram

a graph that compares the properties of stars

main sequence

a narrow band of stars on the HR diagram that runs diagonally from the upper left (bright hot stars) to the lower right (dim cool stars)

Low mass stars

nebula → main sequence yellow star →red giant → planetary nebula → white dwarf → black dwarf

High mass stars

nebula → main sequence blue star → red super giant → supernova → neutron star (over 8 solar masses) →black-hole (over 20 solar masses)

supernova

a massive explosion in which the whole outer portion of a star is blown off

neutron star

a star so dense that only neutrons can exist throughout

black hole

the remnant of a supernova explosion with a gravitational field so strong that nothing can escape its pull

the doppler effect

the displacement of spectral lines produced by a moving source of waves in which there is an apparent upward shift in frequency for observers towards whom the source is approaching and an apparent downward shift in frequency for observers from whom the source is receding.

redshifted

for objects moving away from an observer, the effect of lengthening of their wavelengths toward the red end of the visible spectrum

blueshifted

for objects moving towards an observer, the effect of shortening of their wavelengths toward the blue end of the visible spectrum

big bang theory

the theory that the universe began about 13.8 billion years ago when something unimaginably small and dense suddenly and rapidly expanded to immense size

cosmic microwave background (CMB) radiation

radiation left over from the big bang which fills the universe

dark matter

undetected matter that makes up most of the universe

23% of universe

dark energy

a new kind of dynamical energy fluid or field, something that fills all of space but something whose effect on the expansion of the universe is the opposite of that of matter and normal energy.

73% of universe

number of official constellations listed by IAU

88